draft-ietf-grow-simple-va-07.txt   draft-ietf-grow-simple-va-08.txt 
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Expires: November 30, 2012 Ericsson Expires: November 30, 2012 Ericsson
A. Lo A. Lo
Arista Arista
L. Zhang L. Zhang
UCLA UCLA
X. Xu X. Xu
Huawei Huawei
May 29, 2012 May 29, 2012
Simple Virtual Aggregation (S-VA) Simple Virtual Aggregation (S-VA)
draft-ietf-grow-simple-va-07.txt draft-ietf-grow-simple-va-08.txt
Abstract Abstract
The continued growth in the Default Free Routing Table (DFRT) The continued growth in the Default Free Routing Table (DFRT)
stresses the global routing system in a number of ways. One of the stresses the global routing system in a number of ways. One of the
most costly stresses is FIB size: ISPs often must upgrade router most costly stresses is FIB size: ISPs often must upgrade router
hardware simply because the FIB has run out of space, and router hardware simply because the FIB has run out of space, and router
vendors must design routers that have adequate FIB. vendors must design routers that have adequate FIB.
FIB suppression is an approach to relieving stress on the FIB by NOT FIB suppression is an approach to relieving stress on the FIB by NOT
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Scope of this Document . . . . . . . . . . . . . . . . . . 5 1.1. Scope of this Document . . . . . . . . . . . . . . . . . . 5
1.2. Requirements notation . . . . . . . . . . . . . . . . . . 5 1.2. Requirements notation . . . . . . . . . . . . . . . . . . 5
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Operation of S-VA . . . . . . . . . . . . . . . . . . . . . . 6 2. Operation of S-VA . . . . . . . . . . . . . . . . . . . . . . 6
3. Deployment considerations . . . . . . . . . . . . . . . . . . 7 3. Deployment considerations . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
ISPs today manage constant DFRT growth in a number of ways. One way, ISPs today manage constant DFRT growth in a number of ways. One way,
of course, is for ISPs to upgrade their router hardware before DFRT of course, is for ISPs to upgrade their router hardware before DFRT
growth outstrips the size of the FIB. This is too expensive for many growth outstrips the size of the FIB. This is too expensive for many
ISPs. They would prefer to extend the lifetime of routers whose FIBs ISPs. They would prefer to extend the lifetime of routers whose FIBs
can no longer hold the full DFRT. can no longer hold the full DFRT.
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used for routers that connect to customers which wish to receive the used for routers that connect to customers which wish to receive the
full DFRT. full DFRT.
This draft describes a very simple technique, called Simple Virtual This draft describes a very simple technique, called Simple Virtual
Aggregation (S-VA), that allows any and all edge routers to have Aggregation (S-VA), that allows any and all edge routers to have
substantially reduced FIB requirements even while still advertising substantially reduced FIB requirements even while still advertising
and receiving the full DFRT over BGP. The basic idea is as follows. and receiving the full DFRT over BGP. The basic idea is as follows.
Core routers in the ISP maintain the full DFRT in the FIB and RIB. Core routers in the ISP maintain the full DFRT in the FIB and RIB.
Edge routers maintain the full DFRT in the BGP protocol RIB, but Edge routers maintain the full DFRT in the BGP protocol RIB, but
suppress certain routes from being installed in RIB and FIB tables. suppress certain routes from being installed in RIB and FIB tables.
Edge routers install a default route to core routers, to ABRs which Edge routers may install a default route to core routers, to ABRs
are installed on the POP to core boundary or to the ASBR routers. which are installed on the POP to core boundary or to the ASBR
routers.
S-VA requires no changes to BGP and no changes to any choice of S-VA requires no changes to BGP and no changes to any choice of
forwarding mechanisms in routers. Configuration is extremely simple: forwarding mechanisms in routers. Configuration is extremely simple:
S-VA must be enabled on the edge router which needs to save its RIB S-VA must be enabled on the edge router which needs to save its RIB
and FIB space. In the same time operator must inject into his intra- and FIB space. In the same time operator must inject into his intra-
domain routing a new prefix further called virtual aggregate (VA- domain routing a new prefix further called virtual aggregate (VA-
prefix) which will be used as the aggregate forwarding reference by prefix) which will be used as the aggregate forwarding reference by
the edge routers performing S-VA. Everything else is automatic. the edge routers performing S-VA. Everything else is automatic.
ISPs can deploy FIB suppression autonomously and with no coordination ISPs can deploy FIB suppression autonomously and with no coordination
with neighbor ASes. with neighbor ASes.
In configurations where BGP routes are used to resolve other routes
or where BGP routes are redistributed to other protocols which both
happen via RIB simple-va can rather then suppressing routes before
they are installed in global RIB flag them as "suppress eligible".
That will allow for seamless route resolution or redistribution while
in the same time FIB size will continue to be limited as previously
flagged routes will not be send from RIB to FIB.
1.1. Scope of this Document 1.1. Scope of this Document
The scope of this document is limited to Intra-domain S-VA operation. The scope of this document is limited to Intra-domain S-VA operation.
In other words, the case where a single ISP autonomously operates In other words, the case where a single ISP autonomously operates
S-VA internally without any coordination with neighboring ISPs. S-VA internally without any coordination with neighboring ISPs.
Note that this document assumes that the S-VA "domain" (i.e. the unit Note that this document assumes that the S-VA "domain" (i.e. the unit
of autonomy) is the AS (that is, different ASes run S-VA of autonomy) is the AS (that is, different ASes run S-VA
independently and without coordination). For the remainder of this independently and without coordination). For the remainder of this
document, the terms ISP, AS, and domain are used interchangeably. document, the terms ISP, AS, and domain are used interchangeably.
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are normally fully meshed and do not use route reflection. It are normally fully meshed and do not use route reflection. It
also needs to pointed out that some large networks are also fully also needs to pointed out that some large networks are also fully
meshed today. meshed today.
- Use of add-paths Use of add-paths new BGP encoding will allow to - Use of add-paths Use of add-paths new BGP encoding will allow to
distribute more then one overall best path from RR to each client. distribute more then one overall best path from RR to each client.
- Alternate advertisement of VA-prefix S-VA prefix does not need to - Alternate advertisement of VA-prefix S-VA prefix does not need to
be advertised in BGP. The BGP suppression will happen as long as be advertised in BGP. The BGP suppression will happen as long as
we configure the S-VA with next hop(s) and implementation verifies we configure the S-VA with next hop(s) and implementation verifies
that such VA-prefix is installed in the RIB and FIB. that such VA-prefix is installed in the RIB and FIB.
In some deployment scenarios BGP routes could be used to resolve BGP routes may be used to resolve nexthops for static routes or other
other BGP routes - commonly process called double or multi-level BGP BGP routes. Because the default route does not imply reachability of
recursion. If such recursion involves specific route resolution any destination, a router can be configured not to resolve nexthops
policy a special care must be taken to either automatically or using the default route. In this case, simple-va should not suppress
manually exclude such routes matching given policy from suppression. a route that may be used to resolve a nexthop for another route.
Route resolution over default route is a special case. Most network
operating systems can be configured by the operator to enable route
resolution over default route(s). In simple-va all default routes
are intra-domain routes and their objective it to shift full lookup
from edge router to more powerful pop to core boundary router or exit
ASBR. In those cases simple-va should be configured in concert with
global configuration regarding resolution via default route. In the
event of actually using default for next hop resolution the worse
case scenario is that the packets may be forwarded one more hop then
dropped if more specific destination route is not found there.
Operators are advised to keep effect in mind when choosing a policy
for use of default route for next hop resolution.
Selected BGP routes in the RIB may be redistributed to other Selected BGP routes in the RIB may be redistributed to other
protocols. If they no longer exist in the RIB, they will not be protocols. If they no longer exist in the RIB, they will not be
redistributed. This is especially important when the conditional redistributed. This is especially important when the conditional
redistribution is taking place based on the length of the prefix, redistribution is taking place based on the length of the prefix,
community value etc .. In those cases where redistribution policy is community value etc .. In those cases where redistribution policy is
in place simple-va code should refrain from suppressing prefixes in place simple-va code should refrain from suppressing prefixes
matching such policy. matching such policy.
In the case where operator injects a default at the pop to core A router may originate a network route or an aggregate route into
boundary into the pop or alternatively when intra-domain default BGP. Some addresses covered by such a route may not exist. If this
route is injected into autonomous system by set of ASBRs peering with router were to receive a packet for an unreachable address within an
their upstreams a special care needs to be take to make sure that any originated route, it must not send that packet to the default route.
aggregate subnet is advertised only from the BGP speakers which There are several ways to achieve this. One is to have the FIR
inject the default route and therefor attract traffic to non existing aggregate the routes instead of the FSR. Another is to install a
destinations. This will allow to completely mitigate potential blackhole route for the nonexistent addresses on the originating
forwarding issue while not specific to simple-va, but applicable to router. This issue is not specific to simple-va, but applicable to
the general use of default routes. the general use of default routes.
4. IANA Considerations 4. IANA Considerations
There are no IANA considerations. There are no IANA considerations.
5. Security Considerations 5. Security Considerations
The authors are not aware of any new security considerations due to The authors are not aware of any new security considerations due to
S-VA. S-VA.
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